Every second fifty terabits of data

Junior Researcher Armin Fehr is working at the University of Bern on the upgrade of a large CERN experiment

Image: B. Vogel, CHIPP, Switzerland

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At the Physics Institute at the University of Bern, Armin Fehr and his colleagues have built the future 'Inner Tracker' of the ATLAS detector on a 1 to 1 scale. In the tube on the left, the proton-proton collisions take place. The dark red box shows one of the regions where the Optoboards will be located. (Image: B. Vogel, CHIPP, Switzerland)

From 2026, the performance of the large-scale experiments at the European particle physics laboratory, CERN, in Geneva will be significantly increased. The preliminary work for the upgrade of the large particle accelerator LHC and the associated detectors is currently in full swing. An important contribution is made by the University of Bern, where doctoral student Armin Fehr (26) and his colleagues are working on a component for the ATLAS detector. This component will enable the read-out of the greatly increased data rates from 2026 onwards.

Since 2010, CERN physicists have been exploring the world of elementary particles at the large accelerator ring LHC (Large Hadron Collider). One of the four major experiments at the LHC is called ATLAS. It consists of a detector with the height of a five-story apartment building. With this giant device, scientists are studying the traces of particles that are formed in the LHC during the collision of protons in order to better understand the elementary particles. The ATLAS detector has been operating reliably for almost a decade. The data obtained here led to the discovery of the Higgs particle, the youngest of the known elementary particles.

The LHC and its large experiments ATLAS, CMS, LHCb and ALICE are far from being finished. On the contrary, preparations are currently underway in order to operate the accelerator ring and the connected experiments from the year 2026 onwards with a five to sevenfold higher performance ("high luminosity", short: HL). Then up to seven billion proton-proton collisions per second will take place compared to the current one billion. The upgrade of the LHC to the HL-LHC is a major project that keeps particle physicists around the globe busy. Many of the components for this upgrade have to be specially produced in time for 2026.

Electrical signals are converted

Physicists from the Laboratory for High Energy Physics (LHEP) at the University of Bern are contributing towards a significant component for the upgraded ATLAS detector. There, half a dozen physicists are working on the new Optoboards. These will be used inside the future ATLAS detector to convert electrical signals into optical signals. This signal conversion is vital in enabling the huge amounts of data recorded to leave the detector.

Electric cables are incapable of transmitting the large amount of data that is generated in the detector and therefore the electrical data must be converted into light pulses and read out via fibre optic cables. Fifty terabits (50x1012 bit) of data from the new 'Inner Tracker' (trace detector, one of the sub-detectors of the ATLAS detector) must be processed by these Optoboards per second. This is 5000 times more than the most powerful home routers can handle. The data are then filtered and examined by particle physicists worldwide.

One of the Bern physicists working on the Optoboard system is Armin Fehr. On his desk in the LHEP laboratory lies a printed circuit board (PCB) equipped with electronic components. Fibre optic cables are connected to the board. With this PCB, Armin Fehr studies and develops the future readout tool for the new 'Inner Tracker'. More than a thousand Optoboards must be ready by 2024. These components will then be assembled with additional parts to form the new heart of the redesigned ATLAS detector, due to be ready in 2026.

"It will work!"

Armin Fehr grew up near Schaffhausen. He studied physics and astronomy at the University of Bern and specialised in particle physics. Since April 2018 he is writing his doctoral thesis, which is supervised by Prof. Michele Weber. Fehr makes an important contribution to the construction of the Optoboards for the future ATLAS detector.

Several thousands of physicists and engineers work at the ATLAS experiment. They all trust that the component from Bern - like all other new components of the upgraded detector - will reliably serve from 2026 onwards. Doesn't this expectation put the 26-year-old doctoral student under tremendous pressure? It’s not as bad as all that, Fehr explains, who recovers from his scientific work in his free time by hiking, playing tennis and video games. "The Optoboard has a long history. Hundreds of physicists have participated in the conceptual and technical studies", says Fehr, adding confidently: " It will work! "

In the enclosed questionnaire, Armin Fehr gives an insight into his daily work as a particle physicist.

Armin Fehr gives an insight into his daily work as a particle physicist. (Image: B. Vogel, CHIPP, Switzerland)

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Armin Fehr gives an insight into his daily work as a particle physicist. (Image: B. Vogel, CHIPP, Switzerland)